If you don't have open bays, just about any of those fibred shiny one sided white papers will work for filling grain and adding a little strength, which is all we are trying to accomplish...
I experimented with the gift stuffing paper you crumple up and shove in the bag... cheap no-name stuff I got at BigLots.
Put it on a piece of scrap balsa and built up a full finish with some dope per usual, and it worked fine. As long as it dries tight and dope penetrates it, I'd imagine it would work fine on fully sheeted surfaces.
Now, open bays are probably a whole other story, but I've avoided open bay structures for quite some time now. If I HAD to do open bays again, I'd prolly do like I did on my Avanti. Put a piece of Phil Cartiers SLC film just large enough to cover the open bay and beyond by 1" larger, then put paper over the whole wing. This lets you build a traditional looking finish over the film, and is darn near bullet proof. You can't see where the film stops, it is so thin a coat of dope hides it.
Hope that helps,
EricV